1. Field of the Invention
This invention relates to a hub assembly for a bicycle, more particularly to a hub assembly with a ratchet-and-pawl mechanism to drive rotation of a hub shell in a uni-direction.
2. Description of the Related Art
A conventional hub assembly for a bicycle, such as that disclosed in US 2003/0198419 A1, includes a hub shell mounted on and rotatable relative to a hub axle, a ratchet-and-pawl mechanism disposed inwardly of the hub shell, and a sprocket mounting member coupled with a side of the hub shell through the ratchet-and-pawl mechanism. The mechanism includes an annular ratchet member having an outer threaded surface threadedly engaging the hub shell, and an inner toothed surface disposed to engage pawls which are mounted on a pawl mounting seat that is coupled to rotate with the sprocket mounting member, and a coil spring disposed to bias the pawls to engage the inner toothed surface so as to transmit the drive of the sprocket mounting member to the hub shell in a uni-direction.
The drawbacks of the aforementioned conventional hub assembly are as follows:
1. The pawls and the ratchet member are required to have a sufficient rigidity for purposes of engagement and thus are made of an alloy steel material. In addition, the ratchet member is relatively thick to form the outer threaded surface and the inner toothed surface. Hence, the pawls and the ratchet member are bulky.
2. Since the pawls are biased by the coil spring to engage the inner toothed surface of the ratchet member, the assembly and replacement of the pawls are inconvenient to conduct.